降雨在裂隙型冰水堆积体中的入渗过程

[目的]探究降雨在裂隙型堆积体中的入渗过程,研究降雨条件下土坡内体积含水率、基质吸力、孔压等的变化情况及湿润锋迁移规律,为降雨诱发覆盖层斜坡失稳机理提供理论支持。[方法]针对两类不同结构堆积体土样进行室内模型试验。[结果]均质模型中湿润峰均匀下渗,锋面达测点后引发孔压及体积含水率减小和基质吸力增加;坡顶受降雨影响变化明显,而坡底变化具有累积效应;裂隙构成雨水入渗的优势通道,其底部会形成暂态饱和区,湿润锋面在该区域产生强烈下凹形成渗透"漏斗",促使湿润锋在该区域先期触底;[结论]降雨入渗过程为:(1)均质型:完全入渗→入渗放缓→稳定入渗→饱和入渗;(2)裂隙发育型:完全入渗→局部强烈下渗→补偿加速下渗→水平侧渗。     

黄土地区降雨的优势入渗深度

[目的]分析黄土地区降雨入渗深度,为研究黄土滑坡破坏机理提供依据。[方法]通过现场观测实验监测不同深度土体的含水量变化趋势,并基于颗粒离散元方法对降雨入渗过程进行数值计算。[结果]监测结果表明黄土地区降雨入渗深度不超过1.5m。进一步通过数值计算发现:优势通道入渗的深度和裂缝几何尺寸有关,裂缝越深、越宽,降雨入渗的深度越大,影响范围越广,且裂缝的几何形态随着降雨入渗过程的发展而发生变化。[结论]黄土降雨入渗分为非饱和入渗和优势通道入渗2种,非饱和入渗深度有限,优势通道入渗深度更大,易诱发大规模滑坡灾害。     

降雨入渗作用下秭归向斜核部南段斜坡稳定性评价

[目的]开展降雨条件下湖北省秭归县向斜核部斜坡稳定性评价研究,为政府部门减灾防灾工程提供科学支持,为滑坡灾害的预测和管理提供科学依据。[方法]以耦合了地下水动力学的TRIGRS无限斜坡稳定性计算模型为基础,详细介绍了斜坡稳定性评价的数据处理过程以及参数选取方法。[结果]发生斜坡失稳的区域多位于松散土体中等厚—较厚,地形坡度中等的区域,尤其是土层厚度在7—10m,地形坡度在20°~30°范围内为斜坡失稳高发区。[结论]在土层厚度和地形地貌的双重控制下,短历时强降雨入渗作用导致孔隙水压力增大,这些区域的斜坡土体极易发生滑动,为滑坡危险性较高的多发区域。斜坡稳定性评价结果和滑坡实际分布吻合程度较高,在一定程度上反映出降雨诱发滑坡空间分布关系和分布规律。     

降雨入渗对黄土斜坡土体含水率时空分布特性的影响

为了对降雨入渗引起黄土斜坡土体含水率的变化有较深入的了解,在陕西省延安市宝塔山选取了一个典型的黄土自然斜坡进行土体含水率和降雨联合监测。监测结果表明,斜坡土体中的含水率对降雨入渗的响应具有时间上的滞后性与空间上的差异性。当日降雨量达到10mm或10d累计降雨量达到70mm时,降雨入渗对土体含水率的影响深度小于1.0m;当日降雨量达到50mm或10d累计降雨量达到140mm时,降雨入渗对土体含水率的影响深度小于2.0m。同时,当小时降雨量达到10.4mm时,降雨入渗至0.2m的入渗速率为0.04m/h,由0.2m入渗至1.0m的入渗速率为0.033m/h,降雨入渗速率随着土层深度的增加而减小。     

持续降雨条件下黄土边坡稳定性试验研究

滑坡是黄土丘陵沟壑区常见的重力侵蚀,降雨是黄土边坡失稳的主要诱因。为了研究持续降雨条件下黄土边坡的稳定性,采用人工降雨装置进行室外现场试验,测量土体含水率、密度、滑坡剪切带位置以及裂缝的发育等情况,并使用FLAC3D软件计算模拟持续降雨条件下裂缝发育对边坡稳定性的影响。结果表明:随着降雨历时的增加,黄土边坡土体的含水率逐渐增大,土体强度降低,而且自重增大,坡面冲蚀沟逐渐发育,坡脚出现滑塌,坡顶出现拉裂缝,裂缝加剧了降雨的集中入渗,使得裂缝周边土体强度快速降低,最终导致在降雨历时至308.8 h时发生滑坡,持续降雨和裂缝引起的集中入渗加速了土体强度的降低,导致了滑坡,裂缝发育得越深、数量越多,对边坡稳定性危害越大。研究结果为降雨条件下的黄土边坡稳定分析研究和地质灾害防治提供方法和技术支撑。     

长武塬区降雨入渗特征

为了深入理解深厚黄土层的降雨入渗机制,在黄土高原塬区的长武试验站,应用TDR监测天然降雨下大型土柱土壤含水率的动态变化,并结合土柱底部出流量测定数据,分析天然降雨的入渗特征。结果表明:降雨对土壤含水率的影响主要集中在160 cm深度以上,且随深度增加而递减,至240 cm土层降雨峰值信息几近消失;湿润锋运移速率与降雨强度呈正相关关系,与土壤初始含水率成负相关关系,湿润锋运移深度同降雨量和降雨强度正相关;降雨对300 cm土壤水的补给行为普遍存在,入渗补给以活塞流方式为主;降雨入渗补给土壤水的滞后作用表现出对100～200 cm土壤水的补给滞后时间为15～18 d,对300 cm深度土壤水的补给滞后时间为30～45 d。研究结果对明确黄土塬区水循环机制具有一定参考意义。     

黄土浅层降雨入渗规律研究

[目的]探讨黄土浅层降雨入渗规律,为研究降雨黄土滑坡机理提供理论参考。[方法]以陕西省延安市大路沟滑坡为例,在不同深度裂缝处与非裂缝处布置监测仪器,结合数值模拟手段分析入渗规律。[结果](1)研究区浅层地表通过降雨入渗补给,蒸发排泄。降雨对土体含水量的影响主要体现在土体含水量对降雨的响应时间和响应程度上,存在一定的滞后性,并且随着深度的增加滞后性越明显,蒸发排泄对土体含水量的影响表现在土体的深度和受光面积上,土体的深度越大,土体体积含水量受到蒸发作用影响越小。(2)黄土浅层土体含水量对降雨十分敏感,当降雨量3mm/d时,黄土浅层地表土体含水量基本不受降雨的影响,当3mm/d降雨量40mm/d时,土体含水量随雨水的入渗而变化,并且含水量的变化与降雨量大小成正相关。[结论]由模拟不同工况下雨水入渗过程显示,在雨水入渗过程中,浅层裂缝对降雨入渗深度影响很小,并且研究区黄土入渗深度有限。     

黄土高原旱区浅层黄土水分场的数值分析

[目的]研究黄土高原浅层土体水分场在春季连续干旱条件下的动态变化。[方法]通过非饱和黄土二维非稳态流有限元控制方程对黄土高原浅层土体水分场在不同气象条件下的动态变化进行数值计算。[结果]在连续干旱条件下水分场的计算结果与实测结果较为一致,受蒸发影响的土层最大厚度为1.8m,连续3个月的干旱使其平均含水率降低至7.9%,土壤蒸发强度随着含水率的减小而减小。强度较小且分散的降雨对于缓解连续干旱期黄土高原土壤干旱基本无效,大强度集中降雨只能在短时间内缓解土壤旱情。[结论]数值计算结果可为实际工程中植被类型的选择以及灌溉时间的把握所参考。     

土壤初始含水率对坡面降雨入渗及土壤水分再分布的影响

在防止土壤侵蚀和雨后抑制蒸发的条件下，利用室内人工降雨试验，研究了土壤初始含水率对坡面降雨入渗、湿润锋运移及土壤水分再分布规律的影响。结果表明：初始含水率越高，产流越快，平均入渗率越小，达到稳定入渗率的时间也越短；当初始含水率均匀分布时，降雨入渗和再分布过程中湿润锋面平行坡面垂直向下整体运移，坡面降雨入渗过程可以简化为一维；当初始含水率非均匀分布时，初始含水率越高，再分布过程中湿润锋的运移速率越大，但在降雨入渗过程中，湿润锋的运移速率与土体的湿润程度和范围有一定的关系；坡面上方来水(径流)虽然对湿润锋运移速率影响不大，但对入渗有一定的促进作用；再分布过程中，土壤水分有沿坡向下运移的趋势。     

降雨非饱和入渗对土壤热量运移变化的影响

高温季节土壤表层温度非常高，土壤内部含水率较低，突发性降雨对于土壤温度动态变化和水热交换运移影响极大。为了揭示降雨非饱和入渗对土壤热量运移变化的影响，该研究建立了反映降雨入渗过程的土壤热量运移数学模型，编制了有限元数值计算程序，针对南京雨花台区典型土壤，开展了降雨非饱和入渗对土壤热量运移影响的数值计算与分析研究。结果表明：不考虑降雨入渗情况下，土壤温度变化与热量运移主要是表层土壤与环境之间的热交换作用引起，热量运移影响深度约0.2 m；降雨强度45 mm/h作用下，随降雨历时增加，雨水全部自由入渗到土壤内部，土壤内部基质吸力呈线性递减趋势，湿润锋面逐渐下移，土壤体积含水率快速增加；湿润锋过后的土壤体积含水率逐渐接近于饱和体积含水率，土壤入渗能力逐渐下降，直至趋于饱和入渗率；在降雨非饱和入渗影响下，入渗到土壤孔隙中的低温雨水与土壤颗粒发生热量交换，进而改变了原有土壤温度场分布，并随着降雨入渗深度的持续增加，降雨入渗过程对土壤热量运移的影响呈现逐渐减弱趋势。经过现场实测数据与模拟计算结果验证，随着降雨历时增加，土壤体积含水率实测值和数值计算值相对误差保持在±3.99%以内，均方根误差RMSE为0.01 cm3/cm3；土壤温度实测值和数值计算值的相关误差保持在±2.72%以内，均方根误差RMSE为0.55℃，模拟计算结果和现场实测数据均吻合较好，表明该模型对描述降雨非饱和入渗过程土壤热量运移规律的适应性较强，数值计算程序合理。研究成果可为农业水利工程与水土保持、土壤水文水资源的分布与利用、城市水资源控制与生态环境保护等领域提供重要参考。     

Soil-profile distribution of primary and secondary plant-available nutrients under conventional and no tillage

Nutrient distributions under no tillage (NT) compared with conventional disk-and-bed tillage (CT) management in the warm, humid region of the southeastern USA need to be assessed so that future placement, quantity, and type of fertilizers can be altered, if necessary, to efficiently match crop demands. We determined soil-profile distributions of pH, N, P, S, K, Ca, Mg, Na, Zn, Fe, Mn, and Cu to a depth of 0.9 m at the end of 8.5 years of continuous CT and NT management on a Weswood silty clay loam (fine, mixed, thermic Fluventic Ustochrept) in southcentral Texas. Most dramatic changes occurred within the 0–0.05 m depth, where soil under NT had lower pH, Fe, and Cu than under CT, but greater P, K, Zn, and Mn. Greater P and K under NT than under CT also occurred below the till-zone (0.15–0.3 m). At a depth of 0–0.3 m, soil under NT contained greater amounts of extractable P, K, Zn, Fe, Mn, and Cu than under CT. Nitrogen fertilization had little effect on nutrient distributions, except resulting in greater extractable K at 0–0.05 m and greater nitrate at 0–0.15 m. Few changes in soil-profile distributions were observed for extractable S, Ca, Mg, and Na. Long-term continuous use of NT on this fine-textured, high-fertility (except for N) soil had no apparent adverse effects on nutrient distributions relative to CT, but enhanced conservation and availability of P, K, Zn, Fe, Mn, and Cu near the soil surface where crop roots proliferate.     

Assessing the effectiveness of conservation measures: Resolving the “wicked” problem of the Steller sea lion

“Wicked” problems are those that are complex and that change when solutions are applied. Many conflicts in conservation fall into this category. The study approached the problem of how to constrain the apparent wickedness of a problem in the conservation management of a species by using simple empirical indicators to carry out iterative assessment of the risk to a population and to document how this risk evolves in relation to the addition of new data and the implementation of management actions. Effects of high levels of uncertainty within data and also concerning population structure were examined through stochastic simulation and by exploration of scenarios. Historical trends in the example used, the Steller sea lion, showed rapid declines in abundance in some regions during the 1980s. The current total population is 130,000-150,000 Steller sea lions through Alaska and British Columbia and this number has been stable since about 1990 in spite of regional differences in population dynamics. Regional differences in the sequence of changes in the number of pups and non-pups, suggested that an internal re-distribution of juveniles could have happened between 1980 and 1990. Current productivity also appears close to the long-term mean. Stochastic population projection using various scenarios showed that, based upon this history, the risk of extinction for the population has declined and is below reasonable thresholds for considering the population to be endangered. The trends in risk suggest that management actions taken since 1990 have probably been effective. Consequently, the conservation management objectives for the Steller sea lion are probably being met. The approach provides a mechanism, based upon experience and scenario analysis, for exploring future policy options and may help to constrain the debate amongst stakeholders about the cost-benefit trade-offs associated with different options.     

Enhanced establishment and growth of giant cardon cactus in an eroded field in the Sonoran Desert using native legume trees as nurse plants aided by plant growth-promoting microorganisms and compost

To evaluate the feasibility of long-term desert reforestation technology of mixed vegetation, cardon cactus (Pachycereus pringlei) seedlings from indoor and outdoor nurseries were planted in the field adjacent to one seedling of potential legume nurse trees: mesquite amargo (Prosopis articulata), yellow palo verde (Parkinsonia microphylla), and blue palo verde (Parkinsonia florida). Some of the planting holes were also supplemented with common dairy compost. Additionally, the combinations of legume tree–cactus were inoculated with either a consortium of desert arbuscular mycorrhizal (AM) fungi, plant growth promoting bacteria (PGPB; the diazotroph Azospirillum brasilense Cd, and the phosphate solubilizer Paenibacillus sp.), or a mixture of all. The field experiments were evaluated periodically during 30 months for survival and growth. Cardons reared in an outdoor screen house survived better in the field than those reared in a controlled growth chamber and hardened later outdoors. Association with any legume nurse tree increased survival and enhanced growth of untreated cardons. For cardons growing alone, application of either compost, AM fungi, and all the treatments combined increased survival. For these plants, no treatment affected plant growth during the first 3 months after transplanting. Later, all treatments, except for AM fungi, enhanced plant growth. However, only 2 years after transplanting the enhanced growth effect of AM fungi was also significant. In the presence of the legume nurse trees, transient positive effects on cardon growth were recorded. General evaluation after 30 months of cultivation showed that the treatments positively affected cardon growth when growing alone or in combination only with mesquite amargo but not with the other two legume trees. This study proposes that young legume trees have the capacity to enhance survival and growth of cardon cactus, depending on the legume cactus combination. Additional treatments such as compost or PGPB can either amplify the effect or else attenuate it.     

Karyotypic and genome size variation in Cajanus cajan (L.) Millsp. (pigeonpea) and some wild relatives

Detailed karyotypes and 4C DNA amounts have been studied in five cultivars of Cajanus cajan and 20 species belonging to Cajanus, Rhynchosia, Dunbaria, Flemingia and Paracalyx. C. cajan shows intraspecific variability and its karyotype is most similar to that of C. cajanifolius (sect. Cajanus) in the morphology and number of satellite chromosomes and the lack of any correlation between chromosome size within the complement and asymmetry. Karyotypes of C. lineatus and C. sericeus belonging to sect. Atylia are similar with respect to maximum r-index and the ratio of longest and shortest chromosomes in their respective complements. C. acutifolius (sect. Frutocosa) is distinct in having a very low ratio (1.44) between the longest and the shortest chromosomes, while in C. albicans, C. goensis, C. scarabaeoides (sect. Cantharospermum) there is no chromosome pair with r-index >2.0. C. mollis and C. volubilis (sect. Volubilis) show similarity with regard to ratio between the longest and the shortest chromosomes and a distinct chromosome pair with an arm ratio of 2.7 and C. platycarpus is distinct (sect. Rhynchosoides) in having the smallest ratio (1.36) between the longest and the shortest chromosomes. 4C DNA amounts in Cajanus and Rhynchosia vary between 3.28 pg to 11.69 pg and 4.92 pg to 11.13 pg respectively, while in Dunbaria, Flemingia and Paracalyx these vary between 4.70 and 7:06 pg. In the genus Cajanus karyotypic features and 4C DNA amounts agree with the sectional classification and bring out a close relationship between C. cajan and C. cajanifolius. This is supported by studies based on seed protein patterns, isozyme analysis, trypsin and chymotrypsin inhibitor patterns, RFLP and RAPD data and crossability relationships. A clear relation between DNA amount and abnormalities effecting the extent of pairing and recombination in interspecific hybrids shows the importance of this study in developing future breeding programme involving C. cajan and its wild relatives that are of potential value.     

Effect of some fungicide seed treatments on the survival of Bradyrhizobium japonicum and on the nodulation and yield of soybean [Glycine max. (L) Merr.]

Several commercial fungicide seed treatments were evaluated for their possible effect on the survival of Bradyrhizobium japonicum on seeds and on the nodulation and yield of soybeans in a greenhouse and a field experiment. quinolate Pro (carbendazim and oxine copper), Vitavax 200FF (carboxin and thiram), and Monceren (pencycuron) had a small effect or no effect on the survival of B. japonicum and on the nodulation and yield of soybeans. They can thus be considered compatible with soybean seed inoculation. Germipro UFB (carbendazim and iprodione), Apron 35J (metalaxyl), and Tachigaren (hymexazol) decreased B. japonicum survival and the nodulation and yield of soybeans and thus cannot be considered compatible with soybean seed inoculation.     

Einfluss der düngungsmethoden auf die entwicklung von zuckerrübenkrankheiten

Während neunjähriger (1994-2002) Untersuchungen in der Versuchsanstalt Ba?cyny (Fahlerde, Fall-Gleyboden, ausgebildet aus leichtem Lehmboden) wurde der Befall mit Krankheiten an der Zuckerrübe in Abhängigkeit von der Düngungsmethode bewertet. Folgende Methoden wurden angewendet: A - Mineraldünger, B - Stalldung und Mineraldünger, C - Stroh-, Gründung und Mineraldünger, D - Kompostdünger und Biopräparate (ökologische Düngung). Auf den Objekten A, B, C wurden bei konstanter Phosphor-Kalium-Düngung die Stickstoffgaben von 0 bis 180 kg.ha^?1 differenziert. Auf dem ökologischen Objekt D ohne Mineraldünger wurden statt Stickstoff die Biopräparate P₅₀₀ und P₅₀₁ verabreicht. Der geringste Befall von Krankheiten wurde an der Zuckerrübe auf jenem Objekt festgestellt, das mit Kompost und den Biopräparaten gedüngt worden war. Im Rahmen der konventionellen Düngungsmethoden wurde allgemein die höchste Intensität der Krankheiten an der mit Stroh, Gründung und Mineraldünger gedüngten Zuckerrübe beobachtet. Ausnahmen von dieser Regel bildete das Vorkommen von echtem Mehltau und Keimlingsfäule. Auf den Objekten A, B, C nahm die Intensität der Krankheiten mit der Steigerung der Stickstoffgabe zu. Auch die auf Objekt D verabreichten Biopräparate stimulierten die Entwicklung der Krankheiten. The effect of various fertilization methods on the diseases of sugar beet was estimated on the basis of nine-year studies (1994-2002) conducted in the Experimental Production Farm in Ba?cyny on loess-based, sedimentary-gley, light-clay soil. The following fertilization methods were applied: A - mineral fertilization, B - mineral and manure fertilization, C - straw, green manure and mineral fertilization, D - ecological compost and biodynamic preparations fertilization. In the objects A, B and C fertilized with phosphorus and potassium, various doses of nitrogen ranging from 0 to 180 kg/ha^?1 were used. In the ecological object D, where mineral fertilization was not used, biodynamic preparations P₅₀₀ and P₅₀₁ were applied instead of nitrogen. The lowest ratio of the diseases of sugar beet was observed in the object fertilized with the compost and biodynamic preparations. In view of the conventional fertilization methods, generally the highest incidence of diseases was noted in the sugar beet fertilized with straw, green manure and mineral fertilizers. The exception was the occurrence of powdery mildew and the black leg. In objects A, B and C the incidence of the diseases increased with the increase in nitrogen doses. The applied biodynamical preparations in the object D stimulated the development of diseases too.     

Prospects for control of Pythium damping-off of lettuce with Trichoderma,Gliocladium and Enterobacter spp.

Summary Damping-off of lettuce (Lactuca sativa) caused by Pythium ultimum was studied in pots containing a non-sterile potting mix in the glasshouse. Fifty P. ultimum sporangia g^-1 compost reduced the plant stand to 15% and shoot dry weight to 18%, but this reduction was totally prevented by applying Trichoderma harzianum at 2×10⁵ viable propagules g^-1 potting mix. Gliocladium virens and Enterobacter cloacae also alleviated the damping-off. E. cloacae did not adversely affect the action of the fungal antagonists. The co-existence of the bacterial and fungal antagonists was revealed on the root surface and inner surface of the testa by scanning electron microscopy, indicating the compatibility of the biocontrol agents.     

细菌、真菌及植物氮营养信号研究进展

氮素吸收代谢是所有生物生命活动的核心部分,因此,各种生物对氮的吸收与同化过程都有精细的调节。这种调节依赖于生物对体内氮素状况信号及体外（生长介质中）氮素信号的感受。过去几十年中,在细菌、真菌中已经对氮素营养信号有了较好的研究,而植物中则相对缓慢,但也有了一定的认识。本文重点比较细菌、真菌及植物中氮信号系统的组成,以期为进一步认识植物中的氮信号接受与转导系统提供启示。     

Potential of wild species for genetic enhancement of some semi-arid food crops

Discovery and incorporation of genes from wild species provide means to sustain crop improvement, particularly when levels of resistance in the cultigens are low and virulent strains of pests and pathogens overcome the host plant resistance. The extent of utilization and the potential of the wild genepool for genetic enhancement were reviewed in five important food crops viz. sorghum, pearl millet, chickpea, pigeonpea and groundnut grown in the semi-arid tropics. Introgression from compatible wild germplasm in the primary gene pool resulted in transfer of new cytoplasmic male sterility systems in pearl millet and pigeonpea, development of high protein, cleistogamous flower and dwarf pigeonpea lines and foliar disease resistant groundnut cultivars. Utilization of wild species in secondary and tertiary gene pools has been generally limited due to sterility, restricted recombination or cross incompatibility. Nevertheless, these species are extremely important as they contain high levels of resistance to several important biotic and abiotic stresses. Several of them, like those belonging to the Parasorghum section and the rhizomatous Arachis species are sources of multiple resistances and hold great promise to sustain crop productivity.     

“绿色革命”以来大气CO2浓度升高对C3作物营养品质的影响

自20世纪60年代"绿色革命"以来,育种技术和农耕技术的发展促进了农作物产量的大幅提升,然而作物的营养品质出现下降趋势。在相似的遗传背景下,大气CO_2浓度升高会使单位体积农作物产品的营养元素含量下降,因此"绿色革命"至今,农作物产品的营养元素下降可能受大气CO_2浓度升高影响。通过植物生长箱模拟"绿色革命"初期和目前的大气CO_2浓度水平(310μmol/mol和400μmol/mol),针对主要C_3作物水稻、小麦和大豆,研究"绿色革命"以来大气CO_2浓度升高对其籽粒的C、N、Fe、Zn元素含量的影响,结果表明:CO_2浓度升高对3种作物籽粒的C元素含量几乎没有影响,变化幅度在±1.5%之间;籽粒的N、Fe、Zn元素含量普遍呈现下降趋势,但均未达到显著水平。